Method of providing a clamping band around the bulb of a television picture tube and implosion-free tube manufactured by means of this method



May 19, 1970 l H.l BONGENAARETAL 3,512,234

METHOD OF PROVIDING. A CLAMPING BAND AROUND THE BULB OF *IA TELEVISION PICTURE TUBE AND IMPLOSION-'FREE TUBE MANUFACTURED BY MEANS OF THIS METHOD Filed Sept. 14, 196'? INVENTOR HENDRIK BAONGENAAR WILLEM F. NIENHUIS United States Patent O 3,512,234 METHOD OF PROVIDING A CLAMPING BAND AROUND THE BULB OF A TELEVISION PICTURE TUBE AND IMPLOSION-FREE TUBE MANUFACTURED BY MEANS OF THIS METHOD Hendrik Bongenaar and Willem Fokko Nienhuis, both of Emmasingel, Eindhoven, Netherlands Filed Sept. 14, 1967, Ser. No. 667,702 Claims priority, application Netherlands, Sept. 14, 1966, 6612938 Int. Cl. H01j 9/18 U.S. Cl. 29-25.13 6 Claims ABSTRACT OF THE DISCLOSURE A method of reinforcing a television display tube to eliminate the risk of implosion wherein an intermediate band is provided around a portion of the tube on the side of the mold match line (the greatest cross-section of the tube to the rear of the front face or the tube window) and thereafter providing a clamping band over the intermediate band having a width at most equal to the intermediate band and the projection thereof on 'the glass surface being covered throughout the width by the intermediate band. The clamping band is thereafter stretched to place it under tension and the pressure exerted on the bulb by this clamping band symmetrically and uniformly distributed after which both the intermediate and clamping bands are secured to the glass and each other respectively. 1

The invention relates to a method of providing a clamping band around the bulb of a television picture tube and more particularly to a band which is disposed entirely on the side of the mold match line of the window remote from the front surface of this window. The invention further relates to a television picture tube provided with such a clamping band the part of the bulb located between the front surface and the mold match line of the window being free.

For reasons of mounting technology, it is desirable in certain cases that the part of the bulb of a picture tube located between the front surface and the mold match line of the window should be free with smaller tubes, in which the diagonal of the window is less than 35 cm., a sutlicient freedom of implosion can still be obtained with the known embodiments provided with clamping bands.

With larger tubes, however, these embodiments are no longer satisfactory. For the freedom of implosion is based on the fact that, due to the compression exerted on the glass by the clamping band, this glass cannot deviate at the area of the bulb of maximum cross-section, so that, when cracks occur, the fragments of glass are continuously pressed against each other. Therefore, it is necessary for a comparatively wide strip of the area of maximum cross-section of the bulb to be covered, since the glass at this area must be prevented from deviating to the outside. With tubes, in which the diagonal of the screen exceeds 35 cm., the area between the screen and the mold match line becomes so wide, however, that a clamping band disposed behind the mold match line can no longer prevent the deviation of the glass at the area located between the front surface and the mold match line of the window, so that implosion may occur. It has been found that the risk of implosion can be avoided in these cases only if the clamping band exerts a consider- 3,512,234 Patented May 19, 1970 ably higher pressure on the glass wall than was usual hitherto. Such a clamping band cannot be provided by the conventional methods, however, without taking further steps. For it is necessary that the clamping band should be made of a hard kind of steel, since the band which must be comparatively narrow in order to lit between the mold match line and the sealing edge of the window to the cone, otherwise cannot withstand the required tensile force.

Such a band of hard steel cannot be clamped around the bulb without taking further steps, since the band, when it is stretched, always slightly grates over the glass, as a result of which the glass is very liable to be scratched. Moreover, steps must be taken to ensure that the tensile force in the band is distributed uniformly and symmetrically along the periphery. The friction at the corners may result in great differences in tensile force between the straight sides of the band, especially if the band is interrupted at one point only and hence is tightened at one point. Moreover, irregularities occur on the contact surface between the band and the glass along the periphery and especially at the joint between the ends of the clamping band, as a result of which the pressure exerted by the band on the glass is distributed very unevenly along the periphery. This need not give rise to diiiculties in the known wide tensile bands which are not excessively stressed, since the bands bear on the glass through a wide area, while the spaces between the band and the glass may be filled up by an adhesive. At the high pressure which must be exerted by the narrow clamping bands in the tubes of the types described above, such adhesives may be pressed away, however, so that a direct contact occurs between the band and the glass and hence the glass is liable to become scratched.

The said disadvantages can be avoided by the use of the method according to the invention, by which freedom of implosion can be obtained also with tubes, in which the diagonal of the image surface exceeds 35 cm., while the part of the window located between the mold match line and the front surface is free.

For this purpose, rst an intermediate band is provided around the bulb on the side of the mold match line remote from the front surface of the window, whereupon one or more clamping bands having a width at the most equal to the width of the intermediate band are provided over said intermediate band so that the projection of each clamping band on the glass surface is covered by the intermediate band throughout the width, the clamping band or bands all being stretched and steps being taken by which the pressure exerted on the bulb through the intermediate band by the clamping band or bands is distributed symmetrically and uniformly along the periphery of the bulb, while the intermediate band is xed on the glass, and/ or the clamping band or bands are iixed on the intermediate band preferably by means of an adhesive. The adhesive may extend in the form of a thin layer to the front surface of the window.

A symmetrical and uniform distribution of compression on the bulb can be obtained in different ways, for example, by winding a long strap or steel with the required tensile force into the intermediate band. A few turns are already sufficient. First the beginning of the steel strap can be welded to the intermediate band. Subsequently, the end of the clamping strap can be welded to the underlying turn or turns. As an alternative, use may be made of an interrupted clamping band which is tightened by means of bolts or clamps, a lubricant being provided on the intermediate band at the corners of the window, so that the clamping band can slide over theYY intermediate band and hence the band is stretched more uniformly all around.,Preferably, two interrupted clamping bands are arranged one on the other, the joint being located on opposite straight sides. Y,

Furthermorefa clamping band'may be used which is interrupted at several points, but this is more complicated.

In view of the large'tensile force the clamping band H must be capable of withstanding at the comparatively small width, substantially only YYclamping bands of hardened Ysteel or high-grade steel can be employed.rThe use of an intermediate band of a material which is hard but which nevertheless is :still softer than glass is required to prevent scratching of the glass For itpis not permissible to provide a clamping band of hardened steel directly on the glass and to tighten it, since this may result in scratching'of the glass, which scratches may Vafterwards give rise to cracks so that the bulb becomes leaky.

YThe intermediate band may be interrupted provided that the space between the intermediate band and the glass Wallis filled with a filler material of sufficient hardness. For at the interrupting area, an irregularity is formed on the Contact surface of the intermediate band and the glass which must be eliminated by the said filler material. Moreover, the filler material mustl adhere sufficiently to the metal of the` intermediate band and to the glass so that the band cannot slide off the bulb by shocks and the like. This may also be achieved by roughening the glass surface, in particular at the corners.

However, the intermediate band used is preferably an uninterrupted annular band which is tautly stretched around the bulb. It is then ensured that the dimensions of the band are such that the band, after being provided on the bulb, just sufficiently surrounds the bulb so that the intermediate band, after the clamping band is provided and stretched over it, bears uniformly on the bulb and does not tend to corrugate. This is preferably achieved by heating the intermediate band before slipping it into the bulb, since the tolerances of the glass of the bulbs can then be neutralized. The pressure exerted on the bulb by such a tautly arranged intermediate band before the clamping band is provided, is negligible when compared with the compression required. The llerand adhesive material used may be polyvinyl acetate with polyester, polyurethane or epoxy resin. The clamping band may also be locally coated with such adhesive in order to prevent the band from being displaced over the intermediate band. If desired, the layer of adhesive may extend up to the front surface of the window in order to obtain an additional protection of the free glass surface, but this is not essential to the freedom of implosion. The bands are preferably not provided before the picture tube has otherwise been completely finished, so that the bands need be no longer strongly heated, which could result in a decrease of the tensile force.

The invention will now be described more fully with reference to the drawings, in which:

FIG. 1 is partly a longitudinal sectional view and partly a side elevation of an embodiment of a picture tube in accordance with the invention, and

FIG. 2 shows a detail thereof.

In the figures, reference numeral 1 denotes a substan= tially rectangular window with display screen of a television picture tube which is sealed at 3 to the cone 2. A layer of adhesive 5, by which the intermediate band 6 is stuck to the glass, is appiied to the glass on the side of the meid match line 4 i.e., the greatest cross-section of the bulb, remote from the front surface on the window. In this case, two clamping bands 7 and 7 made of a hard kind of steel such as hardened steel or high-grade steel (chromium-nickel steel), are provided on the intermediate band 6 so that a symmetrically and uniformly distributed compression is exerted on the bulb, for example, by providing a lubricant at the corners between the clamping t 4 band 7 Yand the intermediate band 6, and by disposing the joints on opposite sides. g

The part of the protruding side surface of the window which is located beyond the mold matchgline 4 and on which the bands 6, 7, 7, are clamped, has a surface, at least at the corners of the window, which is substantially parallel to the axis of the tube so that the bands are less liablerto slide off this surface. Y

Owing to the required high compression, it is necessary that this compression :should be distributed along the periphery of the glass as evenly as possible but at any rate symmetrically. Therefore, usetis preferably made of an uninterrupted intermediate band. The pressure is generally at a maximum at the corners and a minimum at the center of the long sides of the window. It may therefore be desirableto provide spacing blocks between the clamping bands and the intermediate bands or between the bulb and the intermediate band in order to increase the pressure on the straight sides, while, when using an interrupted intermediate band (FIG. 2), the interrupting area will be located at the center of a long side so as to overiap. It must be ensured that this interrupting area produces a minimum jumpwise irregularity. For this purpose, the space at this interrupting area 1Q between the :band and the glass is filled with a Vhard adhesive 5.

In general, the clamping band is chosen to be so narrow that it does not cover the sealing seam 3. However, the intermediate band may extend beyond the seam 3 and the space between this band and the glass may be filled at least in part, preferably with a filler material 12 (synthetic resin) which need not 'De identical with the adhesive 5. The fastening lugs 11 are fastened to the intermediate band 6 preferably by riveting c-r welding. The clamping band 7 is tightened by means of a tightening bolt 8.

The intermediate band 6 has a width of, for example, 45 mm. and a thickness of 1.2 mm. and consists of ingot steei, while the two clamping bands arranged one on the other each have a width of i8 mm. and a thickness of 0.8 mm. and consist of hardened carbon steel or highgrade steel (chromium-nickel steel).

Although one embodiment has been described, the invention may also be carried out differently. At any rate, the clamping band must joint the mold match line, also if this band is much narrower than the distance between the mold match line and the sealing seam.

What is claimed is:

1. A method of providing a clamping band around the glass bulb of a `television picture display tube having a window portion sealed to a conical portion in order to eliminate the risk of implosion, said window having a larger cross section than and -spaced from the front surface and said larger cross section remaining free, comprising the steps first providing an intermediate band around the bulb on the side of said larger cross section remote from the front surface of the window, thereafter providing at least one additional clamping band having a width at the most equal to the width of the intermediate band, the projection of each clamping band on the glass surface being covered throughout the width by the intermediate band, thereafter stretching the clamping band while distributing the pressure exerted on the bulb by the clamping band through the intermediate band symmetrically and uniformly along the periphery of the bulb, and securing the intermediate band onto the glass and the clamping band onto the intermediate band.

2. A method as claimed in claim 1, wherein the clamping band is provided on the intermediate band by winding on to it one or more turns of a long strap of steel.

3. A method as claimed in claim 1, wherein a lubricant is provided at the angular points between the clamping band and the intermediate band.

4. A method as claimed in claim 3, wherein the intermediate band is interrupted and is fixed to the glass by means of a layer of an adhesive which extends up to the front surface of the screen.

5 6 5. A method as claimed -in claim 1 wherein an inter 3,162,933 l12/ 1964 Trax et al. 29-25.11 rupted annular intermediate band is heated, is provided 3,220,592 11/ 1965 Powell et al 220-2.1 around the lbulb and after cooling encloses the surface 0f 3,260,397 7 1966 Gier et al 220-2.1 the bulb so that it bears evenly on -the Ibulb after the 3,271,516 9/1966 Damm 220-2.1 clamping band has been provided and tightened. 5 3,314,566 4/ 1967 Minneman et -al 2202.1 6. A method as claimed in claim 1 wherein the mate- 3,317,172 5/ 1967 IBalint 220-2.1

rial of the intermediate band is softer than -the glass of the bulb, While the clamping band consists of a hard JOHN F- CAMPBELLPIIIUQTY EXamlIleI kind of steel.

References Cited lo R. B. LAZARUS, Asslstant Exannner UNITED STATES PATENTS U.S. C1.X.R. 2,785,820 3/1957 Vincentet'al. 22o-2.1 17-8-7.82;220-2.1

2,874,017 2/1959 Henry et al. 178-7.82 

